We now have the results of an internal investigation into the George Washington Bridge lane closure scandal. Today's report was commissioned by the administration of New Jersey Governor Chris Christie, and it finds the governor did nothing wrong. It won't be the last word. Critics question the report's credibility, as NPR's Joel Rose reports.

JOEL ROSE, BYLINE: Investigators conducted more than 70 interviews and combed through hundreds of thousands of documents at a cost to New Jersey taxpayers of $1 million. Lead investigator Randy Mastro says it all points to one conclusion.

RANDY MASTRO: Governor Christie had no involvement in the decision to close these lanes and no prior knowledge of it, not a shred of evidence of it.

ROSE: The report puts the blame for the incident squarely on two people: Bridget Kelly and David Wildstein. Wildstein is the former Christie appointee who carried out the lane closures in Fort Lee, New Jersey. Kelly is the former Christie staffer who approved them.

MASTRO: They had an ulterior motive for implementing that decision to, in some way, target Mayor Sokolich in Fort Lee. We're not able to answer what that ulterior motive was.

ROSE: But Mastro says his team found no evidence that the lane closures were an act of retaliation against Mayor Mark Sokolich, a Democrat, for refusing to endorse the Republican Christie for re-election. Investigators did not talk to Wildstein or Kelly, who are both pleading the Fifth. But there are still a few revelations about them in the report, including the allegation that Wildstein told Governor Chris Christie about the lane closures while they were happening during a public memorial service the two attended on September 11th. But Mastro says the governor doesn't remember their conversation.

MASTRO: It's a common occurrence to have traffic issues, problems in the bridges and tunnels, so it would not have registered with the governor.

ROSE: At times, Mastro sounded a lot like a defense attorney laying out his opening argument to an unusually combative jury. Indeed, critics immediately questioned the report's impartiality. Democrat John Wisniewski is co-chair of the New Jersey legislative committee that's also investigating the lane closures.

JOHN WISNIEWSKI: And it's very difficult to determine who is telling the truth when you don't hear from all side. Lawyers hired by and paid for by the Christie administration will not be the final word on this matter.

ROSE: The internal investigation also dismissed allegations by Hoboken Mayor Dawn Zimmer that the Christie administration threatened to withhold Sandy relief funds unless she approved a private development project. The U.S. attorney's office in New Jersey has its own ongoing investigation. Joel Rose, NPR News. Transcript provided by NPR, Copyright NPR.